1. Field of Invention
This invention relates generally to transducers and more particularly to a Stirling cycle transducer for converting thermal energy into mechanical energy or for converting mechanical energy into thermal energy.
2. Description of Related Art
Stirling cycle heat engines and heat pumps date back to 1816 and have been produced in many different configurations. Potential advantages of such Stirling cycle devices include high efficiency and high reliability. The adoption of Stirling engines has been hampered in part by the cost of high temperature materials, and the difficulty of making high pressure and high temperature reciprocating or rotating gas seals. Furthermore the need for relatively large heat exchangers and low specific power in comparison to internal combustion engines has also hampered widespread adoption of Stirling engines. Specific power refers to output power per unit of mass, volume or area and low specific power results in higher material costs for the engine for a given output power.
Thermoacoustic heat engines are a more recent development, where the inertia of the working gas cannot be ignored as is often done in Stirling engine analysis. In a thermoacoustic engine designs, the inertia of the gas should be accounted for and may dictate the use of a tuned resonator tube in the engine. Unfortunately at reasonable operating frequencies the wavelength of sound waves is however too long to allow for compact engines and consequently results in relatively low specific power. Thermoacoustic engines are however mechanically simpler than conventional Stirling engines and do not require sliding or rotating high-pressure seals.
One variant of the Stirling engine is a diaphragm engine in which flexure of a diaphragm replaces the sliding pistons in conventional Stirling engines thus eliminating mechanical friction and wear. One such apparatus is disclosed in commonly owned PCT Patent application CA 2010/001092 filed on Jul. 12, 2010 and U.S. Provisional Patent application 61/213,760 filed on Jul. 10, 2009, both of which are incorporated herein by reference in their entirety. Diaphragm engines have relatively large radius compared to their height and thus accommodating radial thermal expansion of the hot side relative to the cold side may present challenges.